Electrical characteristics of environmentally friendly insulating oils

In a search for mineral oil substitutes, we investigated the characteristics of environmentally friendly silicone oil and ester oil. The electrical performance was assessed in terms of the breakdown, streaming electrification characteristics and the volume resistivity. The burning characteristics of each oil were also investigated. The temperature dependence of the breakdown voltage in an oil unit and the surface breakdown characteristics in a composite insulating system comprising an insulating oil and an immersed insulator were determined. We also investigated the temperature dependence of the charge density in oil. The charge density in silicone and mineral oils increased with temperature, with maximum values at ~100°C and ~60°C, respectively. By contrast, the charge density in ester oil decreased with increasing temperature and was maximum at ≤ 30°C.